EDTV systems are systems which are designed to transmit and receive television signals and provide the consumer with reproduced images of higher quality than those available from e.g. conventional NTSC systems. In addition it is highly desirable that the EDTV systems utilize conventional broadcast channels and be compatible with existing television receivers, that is, that existing receivers be capable of reproducing an EDTV signal with image quality substantially as good as conventional NTSC.
Two such systems are described in the Feb. 1988 volume of the IEEE Transactions on Consumer Electronics, (Vol. 34, No. 1). The first system is described in the article by Isnardi et al., entitled "Decoding Issues In The ACTV System", at pages 111-120. The second system is described in the article by Yasumoto et al., entitled "A Wide Aspect Ration Television System With Full NTSC Compatibility" at pages 121-127. Both systms originate images in wide screen format, and separately process the center and side portions of the image. Both systems generate a relatively wideband signal including information from the center image portions which is NTSC compatible. In addition both systems generate a relatively narrowband signal containing auxiliary information for producing an enhanced image. The narrowband signal (V-T helper signal) generated in the Isnardi et al. system includes field differential signals for each image frame. This signal is utilized in an EDTV receiver as an aid in generating progressive scan signals with reduced motion artifacts. The narrowband signal (multiplexed signal) generated in the Yasumato et al. system contains composite video information for the side portions of each image.
Both the Isnardi et al. and Yasumato et al. system transmit the wideband signal as a conventional NTSC signal. The narrowband signal is transmitted by quadrature modulating the picture carrier of the wideband signal, so that all of the image information is transmitted in a single channel.
In contemporary broadcast studios for example, video signals are generated in a camera and encoded into NTSC format. Nominally these signals are coupled, over a single broadband conductor, to the various studio processing, switching, special effects, etc. apparatus, and then to the transmitter. To maintain signal integrity much of the studio equipment has 15 MHz or greater signal handling capability. Practically however, the composite signal bandwidth is limited by the bandwidth capability of video tape recorders, (VTR's) which have a signal handling bandwidth of about 6 MHz.
The studio equipment does not have provision for handling the lower bandwidth signals generated in EDTV systems. These signals must be carried around the studio and delivered to the transmitter in parallel with the wideband compatible NTSC signal. At the transmitter the two signals are combined for brbadcasting. In general it would appear that for a studio to handle EDTV signals of the type having separate wideband and narrowband components, duplicate equipment is required for the two signals. This not only doubles the equipment cost to the broadcasters but also creates significant synchronizing and timing problems to maintain the proper relationship between the two signals.
The present invention obviates equipment duplicity and the timing and synchronization problems in an EDTV facility.
In, for example, the Isnardi et al. system higher frequency video information is effectively folded into the 4.2 MHz spectrum bandwidth of composite video signals. As such the wide bandwidth channels (15 MHz) of the studio equipment is under-utilized. In addition the majority of studio equipment is transparent to the makeup of the signal being processed.
Realizing these characteristics of the studio equipment, the present inventors discerned that the bandwidth of the limiting studio components (the 6 MHz bandwidth of VTR's) is sufficient to frequency multiplex the lower bandwidth signal with the higher bandwidth composite signal for transmission through the studio.